The present invention pertains to rotary valves, that is to valves in which a rotatable closure element is mounted in a flowway defined by the valve body so that it may be rotated between its open and closed positions. Examples of such valves are butterfly or disc valves, ball valves, plug valves, globe valves and the like. The valve body of such an assembly, which defines the fluid flowway, particularly in the case of a butterfly or disc valve, is typically provided with an annular seat or seal engageable with the periphery of the disc to seal against fluid leakage when the valve is closed. In many cases, such valve seats may be formed of elastomeric and/or polymeric materials. However, there are numerous situations in which it is necessary, because of the chemical and/or thermal environment in which the valve is to be used to use a seat which is at least partially metallic in nature. Generally speaking, valves which are in environments subject to fire which would virtually destroy a valve seat of an elastomeric and/or polymeric material, have seat assemblies which are composite in nature having a primary sealing section of a polymeric material and a secondary sealing section of metal. Thus, in the event the polymeric sealing section is destroyed by fire, the secondary metal sealing section acts to effectively seal flow through the valve.
In certain prior art "fire safe" valves, it is necessary that the polymeric portion of the seat assembly be completely destroyed in order for the back-up metal sealing portion to be activated. This is clearly undesirable since it is quite likely that only a portion of the polymeric seat will be destroyed in which case the metallic sealing portion will not be activated at all, in which event the valve will leak which can prove to be disastrous.
The metallic sealing section of composite valve seat assemblies typically has some spring characteristics which tend to provide a certain degree of memory. However, in most instances, it is necessary to supplement these inherent properties of the seat. In the past, springs have been employed for this purpose. For example, a coil spring or garter spring might be disposed in generally surrounding relation to the metal seat, or the sealing portion thereof, to provide memory.
Such prior devices suffer from several disadvantages. For example, when used at elevated temperatures, the conventional spring will lose spring temper and cease to properly perform its function of providing memory for the valve seat. Attempts to overcome these disadvantages, while still employing conventional springs, merely result in further complication of the device and undue expense. In co-pending application Ser. No. 344,502, herein incorporated by reference for all purposes, there is disclosed an improved metal seat construction which overcomes most problems associated with prior art metallic seats for rotary valves.